The present invention relates to a refrigerating cycle using a refrigerant containing hydrofluorocarbon as a main component.
FIG. 3 shows an example of a conventional refrigeration unit.
Conventionally, for example, as shown in "Tripologist", vol. 35, No. 9 (1990), pp. 621 to 626, in the case of designing a refrigeration unit with HFC134a refrigerant which is hydrofluorocarbon, compatibility of the refrigerant and refrigerator oil is one of important characteristics, and PAG (polyether) or ester refrigerator oil has been used. FIG. 5 shows a refrigeration unit using HFC134a refrigerant. In FIG. 5, the reference numeral 1 represents a compressor for compressing refrigerant gas; 2, a condenser for condensing high-pressure refrigerant gas ejected from the compressor 1; 3, a capillary tube; 4, an evaporator; 5, a header having a refrigerant quantity adjustment function; and 6, refrigerator oil reserved in the compressor 1 for lubricating a sliding portion of the compressor 1 and sealing a compression room. PAG 6a or ester refrigerator oil 6b is used as the refrigerator oil 6.
Next the operation will be described. The refrigerant compressed by the compressor 1 is ejected into the condenser 2. Here, most of the lubricating oil 6a or 6b used for sealing the compression room and so on is separated in the compressor which uses, for example, a high pressure vessel. That is to say, about 0.5 to 1.0 weight percentage of the oil 6a or 6b relative to the refrigerant is ejected from the compressor 1 together with the refrigerant. Having compatibility or solubility with the refrigerant, the ejected oil 6a or 6b has enough fluidity to return to the compressor 1 through the condenser 2, the capillary tube 3, the evaporator 4 and the header 5. Accordingly there is no case where the lubricating oil 6 disappears from the compressor 1. Therefore, normal lubrication can be realized. In addition, there has been a possibility that the refrigerant foams in so-called sleeping of the refrigerant when the compressor 1 is stopped for a long time.
A conventional refrigeration unit using HFC134a as a refrigerant has such a configuration as described above. The polyether 6a used as refrigerator oil has volume resistivity in a range of from 10.sup.7 to 10.sup.10 .OMEGA..multidot.cm and saturated water content of about 25,000 ppM, and the ester refrigerator oil has improved characteristics such as volume resistivity in a range of from 10.sup.12 to 10.sup.14 .OMEGA..multidot.cm and saturated water content of about 1,500 ppM. However, they show much deteriorated characteristics in electric insulation and moisture absorbing property in comparison with present CFC12 refrigerator oil having characteristics such as volume resistivity of 10.sup.15 .OMEGA..multidot.cm and saturated water content of about 500 ppM. The insulation has a problem relating to long-term reliability of a compressor. As for the moisture absorbing property, also on dealing with assembly parts of the compressor or dealing with the completed compressor, it is necessary to make the saturated water content as small as possible, so that there has been a problem that the dealing is troublesome.
There have also been many problems of dealing on manufacture at the time of assembling a refrigerator, such as reducing the opened time of a refrigerating cycle. In addition, there have been a problem that if a large quantity of water content gets into the refrigerating cycle, the production of sludge is accelerated, or the water content is frozen to close capillary tubes to cause a cooling fault, or the like.
In addition, in a conventional refrigeration unit using HFC134a as a refrigerant, if the refrigerant has high moisture absorbing property, such various problems occur that it becomes difficult to prevent parts of a compressor from getting rusty; that a capillary tube or an expansion valve of a refrigerating air-conditioning apparatus is closed by icing; that moisture accelerates hydrolysis of ester oil so as to produce sludge; that moisture accelerates hydrolysis of polyethylene terephthalate used as insulating material of a motor so as to produce sludge; and so on. In order to prevent these defects, on the process of manufacture, it has been necessary to eliminate moisture in oil and moisture in a refrigerant circuit more carefully than that in a system using CFC12 refrigerant. In addition, in order to increase the moisture capturing ability of a dryer provided in the refrigerant circuit, there has been a problem that it is necessary to provide a larger dryer than a conventional one.
In addition, in a conventional refrigeration system, a liquid refrigerant returns into a compressor vessel through a suction inlet at the time of stopping a compressor, and lubricating oil in the compressor is brought into the refrigeration system from the compressor together with the liquid refrigerant at the time of restarting the compressor. Since the brought lubricating oil is HFC134a refrigerant which is low in compatibility, the brought lubricating oil is difficult to return to the compressor until the quantity of flow (=flow rate) becomes a value not smaller than a predetermined value. Accordingly there has been a problem that compressor troubles occur due to lack of the lubricating oil.